The present invention relates to entry guides for a strip mill and more particularly to entry guides of the character described which are usually employed at each mill stand to guide the lead end of the strip to the bite of the work rolls and to clamp the moving strip when tailing-out and provide strip tension or mill entry tension in a tandem strip mill to minimize tail-end slap.
A very important function of mill entry guides is to restrain the moving strip as the mill finishes rolling a coil and the strip tail-end drops out of the previous mill stand rolls. Previous arrangements of such entry guides have been found to be deficient because they do not provide sufficiently high clamping forces on the moving strip, and they are rather complicated structures which are not sufficiently rugged to withstand repeated rigorous tailing-out operations.
Generally strip threaded through a cold reduction mill is advanced by being pushed by the previous mill stand or a driven pinch roll. Strip is fed into the mill guides which have side guides opened slightly wider than the incoming strip width. In addition, some mills have remote controls to move the side guides a fixed distance when threading and tailing-out each coil.
A positioning cylinder assembly lifts the top platen boards to a maximum open position so that the strip head will enter between the guide platens and then the opening is partially closed before the strip enters the roll bite of the mill stand. Side guide adjustment and platen positioning operations keep the head end of the strip on mill center line and guide the strip into the roll bite as the strip is threaded through the mill.
When tailing-out, the guide platens (which are faced with platen boards for frictional engagement with the moving strip) then clamp the moving strip therebetween causing a drag on the strip. This drag restrains the strip and acts as a damper to prevent the strip tail-end from jumping out of control when interstand tension is relieved as the strip tail-end leaves the previous mill stand. When the clamping force of this tailing-out operation is insufficient (as is the case with previous entry guides), proper back tensioning on the tailing-out end of the strip is not provided causing the tail-end of the strip to be improperly rolled, and as much as 150 feet of strip tail-end must be cut off and scrapped. The use of ever increasing mill line speeds magnifies this problem.
The need for ever larger clamping forces has necessitated the use of extremely large air cylinders which are objectionable, as they take up needed valuable space for other equipment and they still do not provide sufficient clamping forces. High pressure hydraulic cylinders are generally not used nor are they desirable as a substitute because of the possibility of hydraulic fluid leaks getting onto the strip and contaminating the rolling solution.
As an example of past practice, bulky 24-inch bore air cylinders or drive means having approximately a 450 square inch effective pressure application area have been utilized for top board or platen positioning in mill guides in addition to clamping, and sufficient clamping forces still are not realized.
Other problems encountered with previous entry guides are over-complication of design and difficult access for service and maintenance. In addition, their designs are such that the nose of the guide cannot extend as close as desired to the roll bite for feeding a lead end of the strip thereto. Also, when board changes must be made on the platens of the mill guides of the prior art, an undesirable amount of time is required for guide board changes.
A principal object of the present invention is to provide a mill entry guide mechanism and method of clamping strip therein which is devoid of the aforementioned problems and disadvantages.